Statistical Testing and Analysis of Performance Factors in GPS Attitude Determining Systems (ADS)

Charles E. Rodgers and Amy R. Gardner

Abstract:	Under a contract to the U.S. Army Topographic Engineer- ing Center (TEC), Adroit Systems, Inc. is developing three versions of its military GPS Attitude Determining System (ADS). One version is designed to meet the requirements of the Multiple Launch Rocket System (MLRS) and other artillery for determining pointing attitude, position, and time to facilitate “shoot and scoot” tactics. Another version is designed to meet the requirements of the Trailblazer electronic warfare van. It will allow rapid direction finding without surveying or using expensive INS units. A man- pack version that has applications for Forward Observer/ Forward Air Controller (FO/FAC) precise targeting is also being developed. All versions depend on the measurement of GPS carrier phase at three antennas to determine plat- form attitude or pointing angle. The first phase of the development effort involves testing and analysis of the factors that determine the performance of a GPS ADS, Quantization of these factors’ effects will allow the design of more efficient and better performing systems. The next phase consisting of final system design, integration, and acceptance testing will begin in the fall of 1993. Multiple factors in the system design or software contribute to the ADS performance. For example, the amount of car- rier phase measurement error caused by multipath depends on the ADS antennas’ environment, the antenna gain pat- tern, the satellite position relative to the baseplane, and the Signal-to-Noise-Ratio (SNR) of the direct signal. These factors interact during each measurement. Therefore, the tests were designed so statistical analysis could be used to determine each factor’s relative contribution to the mea- sured performance. Adroit, a pioneer in GPS attitude determination research, conducted extensive field testing on GPS ADS perfor- mance under various conditions. Approximately 200,000 measurements were made during 30 days of testing during the spring and summer of 1993. The factors examined dur- ing the tests included multipath, antenna gain and phase center migration, SNR, and satellite geometry effects. Sat- ellite geometry is an important driver of attitude accuracy. The full constellation of GPS satellites enhances the integ- rity and accuracy of GPS ADS. This paper presents the test designs, analysis, and results that have been completed to date. Strategies for improving system performance based on the general test results also will be discussed.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	617 - 623
Cite this article:	Rodgers, Charles E., Gardner, Amy R., "Statistical Testing and Analysis of Performance Factors in GPS Attitude Determining Systems (ADS)," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 617-623.
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